This invention relates to an automatic stop/start-up apparatus of an engine which can quickly recognize that a power assist of brakes has fallen while the engine is automatically stopped and which can also automatically stop and start up the engine so that the intent of a person driving is adequately reflected and the person driving does not feel a sense of incongruity.
Some vehicles are arranged with an automatic stop/start-up control apparatus in order to reduce fuel consumption of an engine mounted on the vehicle. The automatic stop/start-up control apparatus of an engine controls to automatically stop the engine when an automatic stopping condition, that an accelerator pedal is not stepped on, is satisfied during driving of the engine. The automatic stop/start-up control apparatus of an engine controls to automatically start up the engine when an automatic starting-up condition on starting operation is satisfied during driving of the engine.
In addition, some vehicles possess an underpressure assist type brake apparatus as a brake apparatus. The underpressure assist type brake apparatus assists brake power by utilizing intake underpressure of an engine as booster underpressure for a brake booster and increasing brake hydraulic pressure to be generated when a person driving steps on a brake pedal.
In a vehicle possessing this underpressure assist type brake apparatus, when a brake pedal is again stepped on while an engine is automatically stopped by an automatic stop/start-up control apparatus, booster underpressure of a brake booster decreases and intake underpressure goes during an engine stop. Thus there is the problem that an assist power decreases and effectiveness of brakes deteriorates.
Therefore, in general, while an engine is automatically stopped, when booster underpressure becomes equal to or less than a predetermined value, and when a drop of booster underpressure is predicted from the number of times that a brake pedal is stepped on and returned, or from a result of watching pressure and temperature of hydraulic brake fluid, the engine is automatically started up. By this means, a drop in effectiveness of the brakes is prevented.
Incidentally, as an automatic stop/start-up control apparatus of an engine dealing with such problem, there are samples disclosed in published Japanese Application Laid-Open No. 2000-97066 and No. 2000-104586.
The automatic stop/start-up control apparatus for an engine in published Japanese Application Laid-Open No. 2000-97066, controls to hold brake pressure after an engine is stopped, and controls to again start up the engine when a time of holding the brake pressure exceeds a predetermined time.
Another automatic stop/start-up control apparatus for an engine is discussed in published Japanese Application Laid-Open No. 2000-104586. The vehicle has a brake assist means using a vacuum servo system. When booster underpressure of a brake booster deteriorates to less than a predetermined value while an engine is automatically stopped, the control apparatus controls to again start up the engine after cancelled stop control.
However, because the automatic stop/start-up control apparatus for the engine, in published Japanese Application Laid-Open No. 2000-97066, automatically starts up an engine considering the above time as a condition, even if effectiveness of the brakes does not deteriorate, the engine is again started up when the predetermined time passes. Accordingly, there is the inconvenience that fuel consumption of an engine cannot be reduced.
Moreover, because the automatic stop/start-up control apparatus of an engine, in published Japanese Application Laid-Open No. 2000-104586, automatically starts up an engine considering the above booster underpressure as a condition, when the condition that booster underpressure deteriorates to less than a predetermined value was satisfied, a power assist fails or already becomes a lost state. Accordingly, there is a problem caused by a delay in recognition of a drop of power assist of brakes.
In order to obviate or minimize the above inconvenience, the present invention provides an automatic stop/start-up control apparatus for an engine which automatically stops the engine when an automatic stop condition is satisfied while the engine mounted on a vehicle is driven. The control apparatus automatically starts up the engine when an automatic start-up condition is satisfied while start-up of the engine is stopped. The automatic stop/start-up control apparatus includes a power assist detecting means to detect a power assist of an underpressure assist type brake apparatus equipped in the vehicle; and a control means to control so as to automatically start up when a decrease rate per unit time of power assist, which the power assist detecting means detects while the engine is automatically stopped, exceeds a first setting value.
In this invention, the automatic stop/start-up control apparatus controls to automatically start the engine by using the control means when a decreasing rate per unit time of power assist, which the power assist detecting means detects while said engine is automatically stopped, exceeds a first setting value. Accordingly, the automatic stop/start-up control apparatus can recognize early that a power assist has fallen by a decrease of booster underpressure when a brake pedal is again stepped on while the engine is automatically stopped, and at once can automatically start up the engine. By getting brake power, the automatic stop/start-up control apparatus, as compared with a usual state, does not cause a change of operation power and operation feeling for the brakes.